[ELF] Add warnings for various symbols that cannot be ordered

There are a number of different situations when symbols are requested
to be ordered in the --symbol-ordering-file that cannot be ordered for
some reason. To assist with identifying these symbols, and either
tidying up the order file, or the inputs, a number of warnings have
been added. As some users may find these warnings unhelpful, due to how
they use the symbol ordering file, a switch has also been added to
disable these warnings.

The cases where we now warn are:

 * Entries in the order file that don't correspond to any symbol in the input
 * Undefined symbols
 * Absolute symbols
 * Symbols imported from shared objects
 * Symbols that are discarded, due to e.g. --gc-sections or /DISCARD/ linker script sections
 * Multiple of the same entry in the order file

Reviewed by: rafael, ruiu

Differential Revision: https://reviews.llvm.org/D42475

llvm-svn: 325125

1 files changed, 14 insertions, 1 deletions

diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 25740a6863e..e1bac230b8d 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -45,6 +45,7 @@
 #include "lld/Common/TargetOptionsCommandFlags.h"
 #include "lld/Common/Threads.h"
 #include "lld/Common/Version.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/CommandLine.h"
@@ -589,6 +590,16 @@ static int parseInt(StringRef S, opt::Arg *Arg) {
   return V;
 }
 
+// Parse the symbol ordering file and warn for any duplicate entries.
+static std::vector<StringRef> getSymbolOrderingFile(MemoryBufferRef MB) {
+  SetVector<StringRef> Names;
+  for (StringRef S : args::getLines(MB))
+    if (!Names.insert(S) && Config->WarnSymbolOrdering)
+      warn(MB.getBufferIdentifier() + ": duplicate ordered symbol: " + S);
+
+  return Names.takeVector();
+}
+
 // Initializes Config members by the command line options.
 void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   errorHandler().Verbose = Args.hasArg(OPT_verbose);
@@ -677,6 +688,8 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
       Args.hasFlag(OPT_undefined_version, OPT_no_undefined_version, true);
   Config->UnresolvedSymbols = getUnresolvedSymbolPolicy(Args);
   Config->WarnCommon = Args.hasFlag(OPT_warn_common, OPT_no_warn_common, false);
+  Config->WarnSymbolOrdering =
+      Args.hasFlag(OPT_warn_symbol_ordering, OPT_no_warn_symbol_ordering, true);
   Config->ZCombreloc = !hasZOption(Args, "nocombreloc");
   Config->ZExecstack = hasZOption(Args, "execstack");
   Config->ZNocopyreloc = hasZOption(Args, "nocopyreloc");
@@ -767,7 +780,7 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
 
   if (auto *Arg = Args.getLastArg(OPT_symbol_ordering_file))
     if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
-      Config->SymbolOrderingFile = args::getLines(*Buffer);
+      Config->SymbolOrderingFile = getSymbolOrderingFile(*Buffer);
 
   // If --retain-symbol-file is used, we'll keep only the symbols listed in
   // the file and discard all others.